Updated Stock Status Indicators for Silky Sharks in the Eastern Pacific Ocean (Document SAC 06 08b)

Transcription

1 Updated Stock Status Indicators for Silky Sharks in the Eastern Pacific Ocean (Document SAC 06 08b) A. Aires da Silva, C. Lennert Cody, M. N. Maunder, M. Román Verdesoto and M. G. Hinton Comisión Interamericana del Atún tropical Inter American Tropical Tuna Commission (IATTC) 6 th Meeting of the IATTC Scientific Advisory Meeting La Jolla, California (USA), May 2015

2 Outline Outline of talk Background Previous attempt to conduct conventional stock assessment How that brought us to indicators Updated stock status indicators (SSIs) Spatial distribution of silky bycatch per set on floating objects (OBJ) Standardized CPUE from OBJ purse seine sets Standardize indices of presence/absence on DEL and NOA purse seine sets Spatial trends in indicators from purse seine sets on OBJ set Environmental considerations (2014) Summary conclusions

3 Stock assessment: SAC-05 INF-F missing catch in early period

4 Indicators OBJ indicators for silky Indices based on standardized CPUE in PS OBJ were proposed as best indicators for representing silky population trends in the EPO Silky shark Carcharhinus falciformis Dolphin sets School sets Floating-object sets

5 Indicators Spatial distribution of BPS Fltobj sets All sizes Color scale: blue: 0 bps green: <= 2 silky/set yellow: 2 5 silky/set red: > 5 silky/set

6 Standardized CPUE OBJ Indicators

7 Standardized OBJ CPUE Indicators

8 Standardized OBJ CPUE Indicators

9 Comparisons among set types Indicators Mean-scaled index Índice de escala promedio

10 Indicators Environmental considerations NOAA/National Weather Service

11 Indicators Environmental considerations JAN 2013 JAN 2014 MAY 2013 MAY 2014 OCT 2013 OCT 2014 NOAA

12 Indicators Indicators conclusions Silky shark stocks have been depleted to low historic levels when compared to the mid 990s Recent increases in CPUE should be regarded with caution There have been environmental changes in 2014 Increases may reflect increased availability rather than abundance

13 Indicators Indicators conclusions No stock stats target and limit reference points have been developed for silky sharks based on these indicators Harvest control runs have not been develop and tested neither Future research: Management strategy evaluation work (MSE) to identify the reference points and harvest control rules that can achieve conservation goals Management: It is critical that precautionary management be implemented immediately to allow silky shark populations to rebuild

14 QUESTIONS?

15 Conclusions Areas of highest catch rate Weak N S structure Animals south of the equator and near the S. American coast most closely allied with Northern animals Seasonal overlap? Future directions? More satellite tagging More samples from central and western South Pacific Source: John Hyde, NMFS-SWFSC Areas of highest catch rate

16 Source: John Hyde, NMFS-SWFSC

17 SAC-05 INF-F Stock assessment Northern Stock Stock Synthesis model and fishery indicators (standardized CPUE and average sizes) Southern Stock Fishery indicators: standardized CPUE Silky sharks 30 Floating-object sets SmallSize 20 MedSize 20 LargeSize

18 Silky spatial distribution by stage Background bycatch of purse seine tuna fisheries School and dolphin sets Floating object sets Silky sharks 30 Silky sharks 30 Dolphin and School sets Floating-object sets SmallSize SmallSize 20 MedSize 20 MedSize 20 LargeSize LargeSize Small: < 90cm TL Medium: cm TL Large: > 150 cm TL Roman-Verdesoto and Orozco-Zoller, 2005

19 Stock assessment: SAC-05 INF-F data sources obtained

20 Stock assessment: SAC-05 INF-F reconstruction of missing catch

21 Stock assessment: SAC-05 INF-F model fit to length compositions

22 Stock assessment: SAC-05 INF-F selectivities

23 Stock assessment: SAC-05 INF-F model misfit to early CPUE

24 Stock assessment: SAC-05 INF-F model misfit to early CPUE (sensitivities)

25 Stock assessment: SAC-05 INF-F estimated time series

26 Stock assessment - conclusions SAC-05 INF-F Stock assessment was attempted using Stock Synthesis ( ) Improved knowledge on length composition of the catches and selectivities Unfortunately, the model was unable to fit the main index of abundance and therefore the results are not reliable Poor performance of the model was probably due to the incomplete knowledge of the total catch in the EPO, particularly for the early period of the assessment (1990s and early 2000s) An alternative approach is needed to provide management advice Use indicators until information is adequate for a full assessment

27 Fishery indicators ( )

28 Indicators Spatial distribution of BPS Fltobj sets small silky (< 90 cm) Color scale: blue: 0 bps green: <= 1 silky/set yellow: 1 2 silky/set red: > 2 silky/set

29 Indicators Spatial distribution of BPS Fltobj sets medium silky ( cm) Color scale: blue: 0 bps green: <= 1 silky/set yellow: 1 2 silky/set red: > 2 silky/set

30 Indicators Spatial distribution of BPS Fltobj sets large silky (> 150 cm) Color scale: blue: 0 bps green: <= 1 silky/set yellow: 1 2 silky/set red: > 2 silky/set

31 Standardized CPUE-OBJ Indicators

32 Standardized CPUE-OBJ Indicators

33 Standardized CPUE-OBJ Indicators

34 Nominal proportions of positive sets by set type Indicators

35 Comparisons among set types Indicators

36 Average length Indicators

37 Average length Indicators